A hydrocarbon with two sp²-hybridized carbon atoms is ethene, also known as ethylene.
Ethene has the formula C₂H₄ and contains a carbon–carbon double bond. Each carbon forms three sigma bonds in a roughly trigonal-planar arrangement, while the remaining unhybridized p orbitals overlap to create the molecule’s pi bond. This gives ethene its characteristic flat structure and prevents free rotation around the double bond.
Ethene is the simplest alkene and an important industrial starting material. Most large-scale production uses steam cracking, often converting ethane or other hydrocarbons at very high temperatures. A major use is polymerization: many ethene molecules join together to make polyethylene, one of the world’s most widely used plastics.
A common mix-up is ethane, which has only single bonds and sp³-hybridized carbon atoms. Ethyne, or acetylene, has a triple bond and sp-hybridized carbon atoms. Ethene also occurs naturally as a plant hormone, where it helps regulate fruit ripening and flowering.